Net::LDAP::Security(3)User Contributed Perl DocumentatioNet::LDAP::Security(3)NAMENet::LDAP::Security - Security issues with LDAP connections
SYNOPSIS
none
DESCRIPTION
This document discusses various security issues relating to using LDAP
and connecting to LDAP servers, notably how to manage these potential
vulnerabilities:
· do you know that you are connected to the right server
· can someone sniff your passwords/userids from the directory connec‐
tion
· can someone sniff other confidential information from the directory
connection
Net::LDAP provides ways to address these vulnerabilities: through the
use of LDAPS, or LDAPv3 and TLS, and/or the use of SASL. Each of these
will be explained below.
How does an LDAP connection work
A normal LDAPv2 or LDAPv3 connection works by the client connecting
directly to port 389 (by default), and then issuing various LDAP
requests like search, add, etc.
There is no way to guarantee that an LDAP client is connected to the
right LDAP server. Hackers could have poisoned your DNS, so 'ldap.exam‐
ple.com' could be made to point to 'ldap.hacker.com'. Or they could
have installed their own server on the correct machine.
It is in the nature of the LDAP protocol that all information goes
between the client and the server in 'plain text'. This is a term used
by cryptographers to describe unencrypted and recoverable data, so even
though LDAP can transfer binary values like JPEG photographs, audio
clips and X.509 certificates, everything is still considered 'plain
text'.
If these vulnerabilities are an issue to, then you should consider the
other possibilities described below, namely LDAPS, LDAPv3 and TLS, and
SASL.
How does an LDAPS connection work
LDAPS is an unofficial protocol. It is to LDAP what HTTPS is to HTTP,
namely the exact same protocol (but in this case LDAPv2 or LDAPv3) run‐
ning over a secured SSL ("Secure Socket Layer") connection to port 636
(by default).
Not all servers will be configured to listen for LDAPS connections, but
if they do, it will commonly be on a different port from the normal
plain text LDAP port.
Using LDAPS can potentially solve the vulnerabilities described above,
but you should be aware that simply "using" SSL is not a magic bullet
that automatically makes your system "secure".
First of all, LDAPS can solve the problem of verifying that you are
connected to the correct server. When the client and server connect,
they perform a special SSL 'handshake', part of which involves the
server and client exchanging cryptographic keys, which are described
using X.509 certificates. If the client wishes to confirm that it is
connected to the correct server, all it needs to do is verify the
server's certificate which is sent in the handshake. This is done in
two ways:
1 check that the certificate is signed (trusted) by someone that you
trust, and that the certificate hasn't been revoked. For instance,
the server's certificate may have been signed by Verisign
(www.verisign.com), and you decide that you want to trust Verisign
to sign legitimate certificates.
2 check that the least-significant cn RDN in the server's certifi‐
cate's DN is the fully-qualified hostname of the hostname that you
connected to when creating the LDAPS object. For example if the
server is <cn=ldap.example.com,ou=My department,o=My company>, then
the RDN to check is cn=ldap.example.com.
You can do this by using the cafile and capath options when creating a
Net::LDAPS object, and by setting the verify option to 'require'.
To prevent hackers 'sniffing' passwords and other information on your
connection, you also have to make sure the encryption algorithm used by
the SSL connection is good enough. This is also something that gets
decided by the SSL handshake - if the client and server cannot agree on
an acceptable algorithm the connection is not made.
Net::LDAPS will by default use all the algorithms built into your copy
of OpenSSL, except for ones considered to use "low" strength encryp‐
tion, and those using export strength encryption. You can override this
when you create the Net::LDAPS object using the 'ciphers' option.
Once you've made the secure connection, you should also check that the
encryption algorithm that is actually being used is one that you find
acceptable. Broken servers have been observed in the field which 'fail
over' and give you an unencrypted connection, so you ought to check for
that.
How does LDAP and TLS work
SSL is a good solution to many network security problems, but it is not
a standard. The IETF corrected some defects in the SSL mechanism and
published a standard called RFC 2246 which describes TLS ("Transport
Layer Security"), which is simply a cleaned up and standardized version
of SSL.
You can only use TLS with an LDAPv3 server. That is because the stan‐
dard (RFC 2830) for LDAP and TLS requires that the normal LDAP connec‐
tion (ie., on port 389) can be switched on demand from plain text into
a TLS connection. The switching mechanism uses a special extended LDAP
operation, and since these are not legal in LDAPv2, you can only switch
to TLS on an LDAPv3 connection.
So the way you use TLS with LDAPv3 is that you create your normal
LDAPv3 connection using "Net::LDAP::new()", and then you perform the
switch using "Net::LDAP::start_tls()". The "start_tls()" method takes
pretty much the same arguments as "Net::LDAPS::new()", so check above
for details.
How does SASL work
SASL is an authentication framework that can be used by a number of
different Internet services, including LDAPv3. Because it is only a
framework, it doesn't provide any way to authenticate by itself; to
actually authenticate to a service you need to use a specific SASL
mechanism. A number of mechanisms are defined, such as CRAM-MD5.
The use of a mechanism like CRAM-MD5 provides a solution to the pass‐
word sniffing vulnerability, because these mechanisms typically do not
require the user to send across a secret (eg., a password) in the clear
across the network. Instead, authentication is carried out in a clever
way which avoids this, and so prevents passwords from being sniffed.
Net::LDAP supports SASL using the Authen::SASL class. Currently the
only Authen::SASL subclasses (ie., SASL mechanism) available are
CRAM-MD5 and EXTERNAL.
Some SASL mechanisms provide a general solution to the sniffing of all
data on the network vulnerability, as they can negotiate confidential
(ie., encrypted) network connections. Note that this is over and above
any SSL or TLS encryption! Unfortunately, perl's Authen::SASL code can‐
not negotiate this.
SEE ALSO
Net::LDAP, Net::LDAPS, Authen::SASL
ACKNOWLEDGEMENTS
Jim Dutton <jimd@dutton3.it.siu.edu> provided lots of useful feedback
on the early drafts.
AUTHOR
Chris Ridd <chris.ridd@isode.com>
Please report any bugs, or post any suggestions, to the perl-ldap mail‐
ing list <perl-ldap@perl.org>.
COPYRIGHT
Copyright (c) 2001-2004 Chris Ridd. All rights reserved. This program
is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
perl v5.8.8 2005-04-25 Net::LDAP::Security(3)